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Wednesday, October 31, 2007

Tonight, I found a message by my mum on my mailbox - she was quite excited and told me that I should absolutely have a look at this new comet, I probably would have heard about it, and that it was such a great view, so well visible now, have a look at the constellation of Perseus...

Comet Holmes, not in my skylight,but photographed at 0800 UT on October 30, 2007 at Costa Mesa, California - via Wikipedia.Now, the net has been fullofreportsaboutcomet Holmes these last days. However, I hadn't really taken note of it - but tonight, the sky above Frankfurt was clear, just a bit misty, bright stars and constellations are clearly visible, and Perseus was close to the zenith - so I looked out of the skylight, and there was comet Holmes: A grey blob to the naked eye, and a quite impressive grey blob in Sabine's grandfather's old binoculars! There is no tail yet, but the blob has some structure, and the comet is bigger than Halley at it's return in 1985/86.

You can find the comet roughly halfway between the bright star Capella in the northern sky and the W of Cassiopeia - have a look at the sky map from heavens above, for example. It's impressive!

Tuesday, October 30, 2007

I'm still kind of stressed out and don't come around to finishing a couple of posts that have been stuck in draft stage for a while. I am having fun answering emails the whole day from workshop speakers who want to know whether there will be chalk in the seminar room, or are worried whether they will get dinner in Waterloo after 10pm (a justified worry btw). No, I like that, I'm serious, makes me feel so important. Either way, some interesting things I came across lately:

Sunday, October 28, 2007

I've always found diagrams helpful to clarify my thoughts. Does anybody of you have experience with the currently available online tools for mind maps? I've come across one or the other, but they didn't impress me much, i.e. I'd prefer an old fashioned notepad over them. Either way, here is what was on my mind this day: the interrelationship between Information Technology (IT), Science and the Society

Any feedback, comments, crititcism is welcome. Is this somehow helpful? Interesting? Well structured? Readable? Thought stimulating? Other adjectives?

The quotation above the upper left arrow refers to the following:

"Science is the only news. When you scan through a newspaper or magazine, all the human interest stuff is the same old he-said-she-said, the politics and economics the same sorry cyclic dramas, the fashions a pathetic illusion of newness, and even the technology is predictable if you know the science. Human nature doesn't change much; science does, and the change accrues, altering the world irreversibly.''

Saturday, October 27, 2007

Only little more than one week to go to our workshop on 'Experimental Search for Quantum Gravity'. If you recall earlier mentioning of my planning for this event, this is the workshop that originally was titled something with 'phenomenology'. However, in times where people seriously talk about 'qualitative predictions', and 'phenomenology' is turning into a widely abused advertisement slogan, I felt like I had to make really clear what I meant. In addition, 'experimental' is easier to pronounce than 'phenomenological'.

Last week I had a temporary crisis, when two of the speakers eventually decided to turn 'to be confirmed' into 'cancelled', only two weeks before the workshop, couldn't they have made up their mind somewhat earlier? (Okay, in case of Brian Greene that was unsurprising, but annoying nevertheless). Then the next day, another one of the speakers who I was very interested in meeting found out he would not be able to get a visa in time. While I was stuck at JFK, arguing with the Delta personnel to rebook me onto the next flight to Toronto, I thought about just taking the first flight to somewhere and let the stupid workshop organize itself.

Instead I got the asshole seat on the Toronto flight, first row aisle, opposite to the restrooms, next to a guy who was barely able to squeeze himself into his seat, had probably be counting on occupying mine as well, and was therefore in a particularly good mood.

That's why I am proud to say that by today, I have managed to replace cancellations, rearrange the schedule, and was able to reduce the number of talks about the all-time favourite topic 'TBA' to four. After one of the initial organizers moved to Europe in September, our workshop is now entirely organized by Germans. Which is kind of funny, because the following weekend workshop on 'Effective Models of Quantum Gravity'is entirely organized by Italians (our schedule, their schedule).

Now that things are taking at least some shape, I am really looking forward to the workshop. We have a couple of very interesting talks, and the participants will make for a good mixture, the intention being to get people together who have been working on various aspects of the same problem. PI's public lecture will also fall into this week which is a nice coincidence. It will be held by John Ellis about "The Large Hadron Collider - World's Most Powerful Microscope" (sounds familiar?). I had some fun with the poster, mostly because I carefully made the layout for ISO paper size which then looked like a disaster on flyers in letter format.

Boah, we are SO organized, we even have a summary talk! After I mentioned it would be nice to have a summary the last day, somebody obviously suggested I'd do it. I then suggested somebody else, who suggested somebody else ... etc ... and eventually somebody suggested Lee. Who, to everybody's surprise (after ignoring the question twice) said yes. (Now every time I see him looking at the schedule he is surprised that he gives the summary talk.) Either way, I am not sure how much time I will have to actually report on the workshop, but the talks will all be recorded, and I will make sure they will appear on the websites as soon as possible.

If it has a title, I don't know it. As far as I am concerned, it is a significant improvement over the previous one. Just that I don't know what this one is supposed to tell me either. I mean, if we want triangulations on our walls, I would prefer a large print of the Loops '05 poster, which I find has higher artistic value.

But I am just an ignorant layperson with an unqualified opinion. Yesterday, I asked some colleagues what they think about the new painting. I got eyes rolled to heaven, and somebody who I don't want to name said it looks like color exercises in high school. The only association I had standing in front of the painting was the price for silver acrylic color. (It's hard to see on the photo, but the lighter shapes on the right side are silver).

"So far, so good" said then men who fell off the roof when he passed the 3rd floor. Threshold effects are quite common in everyday life. They are characterized by a sudden change in a system's properties, like e.g. the ability of a medium to emit laser light, our your brain hitting concrete. In real life, the existence of a threshold is often obvious, but our inability to predict exactly when and how it will be reached fools us into pleasant ignorance, and permanent postponement. After all, tomorrow is another day.

In reality, there is nothing truly infinite, and nothing lasts forever. You won't survive an arbitrary blood alcohol level, no matter how cool you are. Your cat won't live forever, and your boss is not infinitely patient. Warnings to mind these constraints of reality are common knowledge, it's the drop that makes a vase overflow, and the last straw that breaks the camel's back [1].

Yet we are living in a society that disregards its limits. There is no doubt growth can't proceed forever, energy resources are not infinite, and more is not always better. Sure, one can debate exactly when and how a change will set in, but there is no way disregarding the fact that we have to address these problems, and we should do so rather sooner than later.

In his latest book "The Upside of Down" Thomas Homer-Dixon addresses the question of how crucial energy resources are for our societies to maintain their complexity. In a nutshell the argument is that it takes energy to keep our systems running at high performance. We are not prepared to cope with less energy, and our societies' networks lack resilience. Should energy supply dwindle, and one or two unfortunate events hit at the wrong time, the effect can be disastrous. The book is a warning, a call for caution and for action.

Just consider how much you have come to rely on the omnipresent availability of electricity and the internet in your daily life. Now knock out some of the DNS servers, Google, and a couple of telecommunication switches [2]. You think you can cope with that? Sure, but how much of your grocery store's shipment and organization will be affected, your airport's flight schedules, public transportation, traffic reports, online banking, library access, the stock market, how much does your local government rely on email, BlackBerries, WLAN, cellphones? How much of that could suddenly become dysfunctional?

How much can a system take before it breaks down?

"The Upside of Down" is a very clearly written book that lays down all the arguments in a well structured, and accessible manner. One fourth of the book is an extensive list of references and footnotes where the interested reader can check on the details. It is a summary of a large number of works that have been made during the last decades. Homer-Dixon addresses all the obvious objections that people would raise, like e.g. the common optimist objection: things will work out because they have always worked out, people must have believed their situation equally unstable all along. This objection fails to acknowledge that the recent technological developments occur so rapidly that we reach the limits of how we can fix problems in a timely manner:

"Some skeptics might respond that people have always perceived they lived on the cusp of chaos, but in the end they’ve usually managed well by marshaling their ingenuity and courage. But today’s world is fundamentally different from the past. The complexity and speed of our social and technological systems are unlike anything we’ve seen before, and these factors are now pushing against the upper limits of the human brain’s abilities. Ecologically, for the first time in history, we are moving materials, producing energy, and generating waste on a scale that rivals nature itself."[Thomas Homer-Dixon, 'A world that turns too fast', Financial Times, London, Jan 2001]

Of Up

There are various minor points in which I disagree with the author's conclusions, but overall seen the book expresses my unqualified opinion on these issues much clearer and better founded than I could ever have done. Like my feeling that the present organization of our so-called civilized society is an accident waiting to happen. Fortunately, Homer-Dixon doesn't make excessive use of complicated words which often leads me to throw away books about political and social theories. In fact, he uses a lot of explanations from natural sciences that - for obvious reasons - immediately appeal to me. He writes nicely, though the literary style is not exactly terribly good or original. Some of the explanations are rather lengthy, like endless pages on how the Romans build aqueducts or whatever. (Sorry, I've never been a huge fan of the Roman history.)

In the last some chapters he turns towards the question how the laid-out problems can be addressed, and he argues that we need more awareness for the instability of our present systems:

"So somehow we have to find the middle ground between dangerous rigidity and catastrophic collapse. In our organizations, social and political systems, and individual lives, we need to create the possibility for what computer programmers and disaster planers call 'graceful' failure. When a system fails gracefully, damage is limited, and options for recovery are preserved." [p. 291]

And he mentions the obvious questions that have to be answered:

"In countries that are already very rich, we especially need to figure out if there are feasible alternatives to our hidebound commitment to economic growth, because it's becoming increasingly clear that endless material growth is incompatible with the long-term viability of Earth's environment. What might a 'steady-state' economy - an economy that maintains a roughly constant output of goods and services - look like? What economic and ethical values might it be based on? Could it incorporate some (albeit radically transformed version) of market-based capitalism, and would it be compatibility with political and personal liberty? And how would we deal with the political and social conflicts that would inevitably arise if there were no growth?"[p. 293]

And points out that we need to look for alternatives how to organize our societies, possibly with the help of new technologies

"Alternative values might also promote a broader, fairer, and more vigorous democracy, maybe using some kind of open-source approach. New forms of democracy are essential, because we need as many heads as possible working together to solve our common problems, and because the larger the number of people involved in making crucial decisions that affect everyone, the less likely that narrow elite interest will dominate." [p. 306]

(I disagree on the last point about the large number of people, just so you know.) However, I have to say that all this is well and good, but it doesn't strike me as very practical. I mean, telling people to think usually isn't sufficient.

I am not an expert in this field, so it is not clear to me how much of what he says is actually new, or result of his own research. But nevertheless, it is one of these books where upon reading I can only ask myself: what does it say about our society that all these problems are known, have been known since decades, have been well researched, published, pointed out, again and again. But nobody listens. After all, tomorrow is another day. Three more floors to go. So far, so good.

Overall, the book is very recommendable. If this was an amazon review I'd give five stars.

Related: See also my opinion on Global Warming About the author: Thomas Homer-Dixon was born in Victoria, British Columbia and received his B.A. in political science from Carleton University in 1980 and his Ph.D. from MIT in international relations and defense and arms control policy in 1989. He then moved to the University of Toronto to lead several research projects studying the links between environmental stress and violence in developing countries. Recently, his research has focused on threats to global security in the 21st century and on how societies adapt to complex economic, ecological, and technological change. Thomas Homer-Dixon holds the George Ignatieff Chair of Peace and Conflict Studies at the Trudeau Centre for Peace and Conflict Studies at University College, University of Toronto. [Info from this website].[1] The respective German sayings are: Der Tropfen, der das Faß zum Überlaufen bringt, und der Krug der so lange zum Brunnen geht, bis er bricht. [2] Looking forward to the next major earthquake in San Francisco.TAGS:BOOKS, POLITICS, SCIENCE AND SOCIETY

Tuesday, October 23, 2007

Sometimes it is argued that living in a city alienates people from nature, and that, for example, the conscious experience of the course of seasons gets lost. There may be snow on the streets on a few mornings, or the colour of the leaves on the trees changes from green to red, but otherwise, it's just the length of daylight and the average temperature that distiguishes summer from winter.

However, if you keep your eyes open, city landscapes with skyscrapers and big buildings offer quite unexpected, archaic means to follow the course of the seasons, and allow even to establish some primitive forms of calendars.

For example, a few years ago, I was quite fascinated to discover that in the weeks around the summer solstice, the late evening Sun casts the distinctive shadow of a tall hotel building in my neighbourhood onto one of the bank towers in downtown Frankfurt, just before setting behind the Taunus crest. Another bank building erected a few years ago, which now blocks the afternoon Sun from our apartment, serves as a giant screen for the shadow of the same hotel tower just at sunrise around the equinox.

And about four weeks after the fall equinox and before the vernal equinox, I can witness kind of a solar eclipse in the late morning from the kitchen window: For a few minutes, the Sun disappears behind the pyramidal tip of the Messeturm:

At 9:58 in the morning,the Sun disappears behindthe tip of the Messeturm.Eight minutes later, at 10:06,it reappears again, the eclipse is over.

On Sunday, October 14, the Sun's arc was still so high that its disk just touched the very tip of the tower. I couldn't make any observations over the week, and this Saturday, when the photos were taken, the path of the Sun crossed already behind the base of the pyramid. I usually try to observe this "event" each fall and spring, and now I know, we are around October 20.

The idea is really cute. First, let me summarize some basics: Numerous results lead us to expect that black holes emit thermal radiation with a temperature proportional to the inverse of the black hole's mass. This means the more mass the hole looses through the radiation, the hotter it becomes. It is unknown whether a collapse into a black hole, and a subsequent complete evaporation really destroys information about the initial state. This process can also violate certain conservation laws like baryon number. But electric charge, as well as energy and other gauge charges are conserved. However, in standard General Relativity black holes have no 'hair', i.e. the asymptotic solution is completely characterized by only their mass, angular momentum, and electromagnetic charges. So their ability to carry additional gauge charges is limited, unless one allows for quantum 'hair' that resides on the horizon [1]. Though this quantum hair does not have long-range fields, its gauge charge is a conserved quantity.

Now consider a black hole with N different such conserved charges, and assume that these charges are (as is the case for the electric charge as well) each bound to massive particles, the lightest of which has a typical mass Λ. Imagine we set up a black hole that carries these charges, one of each, and we let it completely evaporate. During this evaporation, all the N charges need to be re-emitted somehow. But the black hole's temperature has to be high enough - or the mass has to be small enough respectively - before it can start evaporating off the massive particles. The required temperature is T ~ Λ, or the black hole mass is M~mp2/Λ, where mp is the Planck mass and roughly ~ 1016 TeV. To give you a feeling for these numbers: if we were talking about electric charge, the lightest particle is the electron with a mass of roughly .5 MeV, then the black hole can start evaporating off electric charge if its mass has fallen to ~ 1017 g.

However, there is also an obvious limit to this: the black hole needs to be able to provide the mass of the particles. If the black hole was charged but lighter than an electron it couldn't emit the charge no matter what [2]. If there were many different charges carried by particles with mass scale Λ, one comes to the conclusion that a bound results. The bound arises from the fact that after the black hole started evaporating off the charges, its mass must still have been high enough to provide all the N particles with mass Λ. One thus has N Λ ≤ M, or, if one inserts the above expression for the mass at which the emission of massive particles can start, one finds Λ2 ≤ mp2/N.

The further argument is now the following. We don't know why the gravitational interaction is so much weaker than the other interactions of the standard model (SM). Or, to put it differently, we don't know why the masses of the SM particles are so much smaller than the Planck mass. If we take Λ to be the typical mass of SM particles (Higgs VEV) then there is a gap of roughly sixteen orders of magnitude. Dvali's inequality says if there were very many species particles, then there would necessarily have to be such a hierarchy. Putting in some numbers one finds the 'large' number is indeed very large, and somewhere around N~1032.

Now, as far as I am concerned this doesn't really 'solve' the hierarchy problem, one has just moved it elsewhere (as one also does with the extra dimensional models). Instead of having to explain the gap in the mass-scales one now has to explain where all the other particles are, and why so many of them? However, one can model these as only gravitationally interacting with our beloved standard model which would then only describe a tiny fraction of all there is. The question is of course why there don't seem to exist many particles of this kind around us. But this must stem from some processes in the very early universe, and inflation can easily make small numbers large, and blow up initially only subtle differences. Though it is hard to say at this stage whether it would actually work as desired, I can imagine that such a reformulation of the problem offers the possibility to find a dynamical explanation.

The signatures of such a scenario are in certain regards quite similar to those of extra dimensional models. One has a lot of only very weakly interacting particles whose coupling is given by the Planck mass. But since there are so many of them, their phase space gets really large, cancels the Planck suppression, and the signatures could become observable somewhere around the scale Λ. In contrast to the KK-tower in extra dimensional models however, here the number of species is really finite, so one doesn't have the problem of divergences in the higher dimensional integrals.

I can't say I particularly like the idea of having 1032 particle species, but I like the paper because it is another example for how thought experiments with black holes can lead to sometimes surprising insights. It's a cute idea to play around with that resides somewhere between General Relativity and particle physics, which is - still - a region of large mysteries.

What that has to do with the arrow of time however, I honestly don't know.[1] A black hole can e.g. carry quantum hair associated with discrete gauge charges. This can happen when a local continuous gauge symmetry is broken down to a residual discrete subgroup. See ref [1] in Dvali's paper.[2] However, since the electron mass is so much smaller than the Planck scale, such a black hole would long fall into the quantum gravity regime and no reliable statements can be made anyhow.TAGS:PHYSICS, BLACK HOLES

Friday, October 19, 2007

I am back to Canada after a couple of days in New York City at the workshop Origin of Time's Arrow. The workshop was a whirl of interesting talks, though the least of them had much to do with... oohm... what was the topic again? Most speakers talked about their current research, and just added a last slide with the remark: To come back to the arrow of time...

That is to say I still don't understand all the aspects of the problem. In fact, I am even more confused now. There's nothing as great as explaining why a problem is or isn't a problem without explaining the problem. I had been counting on Andreas Albrecht's talk, but he changed the topic and talked about something completely different (I forgot what). I will tell you some details about the talks I kept in good memory maybe next week, e.g. Gia Dvali's talk was really neat, and besides giving a very entertaining presentation Paul Davies made some interesting points.

At the workshop, I further met the inimitable Mike Kavic from Virgina who wants me to mention him "in a favorable light", and doesn't want me to mention he found at least one of the speakers on the panel discussion must have been drunk, so I won't. He reported from a dinner (which I unfortunately missed but couldn't have afforded anyhow) that another workshop speaker had sufficient drinks to underline arguments by throwing with rolls. See, some academics know how to deal with temporary withdrawal from their guilty pleasures, like new texbooks and other illegal substances.

Since it was my first time in NYC, I stayed a day longer to do some of the tourist stuff etc. In the morning I had received an email from D. who wrote me she went into a bookstore, saw Lee Smolin's book, bought the book, did a Google search, came on my blog, my website, and found the link to my gallery is broken. After we exchanged some emails about this and that, it turned out she lives in Manhattan, and was about to go to the library - while I was in the Museum of Modern Arts just across the street. So I was lucky to have a local tourist guide for the afternoon, and quite an interesting discussion in addition. She also took the photo below, in front of the ice rink at Rockefeller Center

Yesterday I unfortunately missed my flight back to Toronto due to a series of mishappenings caused by my own stupidity and my inability to understand the announcements in the train. Next to me sat a guy who talked to himself all the time, and didn't look like a reliable source of information. Across me sat a black women with a pile of leaflets featuring suspiciously happily smiling people. Upon my question how I get to JFK she said she don't know nothin sista, but if I give her 5 bucks she'd pray for me. Well, maybe I should have done that because the result was I had to sit around at JFK for the rest of the day, where I spent an awful amount of time trying to recall my t-mobile password.

But the most fun was the US border post who checked my documents. He flipped through the expired US visas in my passport: "If you don't mind me asking, miss, what field is it you have your doctorate in?" - "Physics," I said, "Theoretical physics." He made big eyes and said: "Ooooh, theological physics, you must be really smart then."

Thursday, October 18, 2007

A small present I had been offered for my birthday a few weeks ago is a nice little gadget, a keyring pendant with a small lamp which delivers an intense blue light. Not that this little torch light is something completely indispensable, but I like it, just because...

I like it because the blue light conveys so glaringly a development that has taken place over the last 10 years or so, and that has brought a new electronic device from the alchemist-like labs of experimental semiconductor research to the mass-fabrication for give-aways: the blue light-emitting diode.

A light-emitting diode, or LED for short, is a special kind of semiconductor device. And the intense blue light of the small torch is not created by an incandescent lamp, but in such a solid-state semiconductor device.

In chunks of matter that consist of large amounts of atoms, the energy levels of the electrons are not arranged in discrete steps, as in an isolated atom, but are merged into bands. The most important bands are the conduction band, which can contain mobile electrons which can sustain an electrical current, and the valence band, which is usually completely filled with electrons and does not contribute to the electrical current. A semiconductor is a material with a gap between the valence and conduction bands and where at zero temperature, the valence band is completely filled, while the the conduction band is completely empty. This means that there are no electrons available which can carry a current, and that the material is an insulator. However, if the temperature rises, some electrons can be excited across the gap into the conduction band, and those electrons can transport a current. Thus, a semiconductor is a material whose electric resistivity drops with increasing temperature.

The electrical conductivity of a semiconductor can be increased by inserting impurities in the material: atoms that have more, or less, electrons than the atoms of the semiconducting material, and thus offer extra electrons which can populated the conduction band, or "suck" electrons out of the valence band, creating holes in the valence band. This way to insert extra electrons or of holes is called n- or p-type doping, respectively.

Now, if a n-doped and a p-doped semiconductor are brought into contact and an electrical current is driven across the junction by an externally applied voltage, the surplus electrons and the holes run into each other and can recombine, setting free an amount of energy roughly corresponding to the band gap. If the electron and the hole have the same momentum, this energy can be carried away by a photon, and the device emits light - it's a LED. The requirement of equal momentum is both crucial and restrictive and has as a consequence that only some n-p junctions can be used as LEDs. Typically, a maximum of the valence band has to occur at the same momentum as a minimum in the conduction band. Such a feature of the band structure is called a direct gap, and the width of the direct gap determines the colour of the light emitted by the LED.

The band structure of Gallium nitride (GaN) has a direct gap with a width of roughly 3.4 eV, corresponding to a wavelength of 365 nm in the near ultraviolet. (Source: S. Bloom et al, Phys. Status Solidi (b) 66 (1974) 161; via Landolt-Börnstein III/41A1b).

While semiconducting materials with direct band gaps corresponding to red light have been easy to handle and produce since quite a while, creating devices for the production of blue light turned out to be much more complicated. A material with a suitable band gap is Gallium nitride (GaN). The figure shows the band structure of GaN, i.e. the energy of electrons as a function of momentum. The different labels along the momentum axis denote special points in the Brillouin zone of GaN. There is a direct band gap at the so-called Gamma point, which corresponds to electrons (and holes) with zero momentum. Such a direct gap at the Gamma point is ideally suited for the use in LEDs, and the width of the gap 3.4 eV means that the light emitted will be ultraviolet, with a wavelength of 365 nm. So, this looks like an ideal material to build blue LEDs, and indeed, GaN is at the base of today's LEDs, such as those in my little lamp.

Shuji Nakamura at his deskat UCSB Santa BarbaraHowever, there are some caveats: techniques to grow suitable films of GaN had to be found, as had methods to dope the material. The number of defects had to be reduced as much as possible, since defects trigger the recombination of electrons and holes without the production of light. The first LED emitting blue light with high efficiency over a longer time was finally developed in 1993 by a small team lead by Shuji Nakamura at the Japanese company Nichia Chemical Industries. They had grown a quite complicated, layered structure of GaN, AlGaN, and InGaN, and thus laid the foundation for a tremendously growing business:

Blue LEDs based on InGaAs are now very reliable and comparably cheap to produce. They are used in displays, beamers, for lighting, indicator lights, and advertisements. Used in combination with red, amber and green LEDs, they produce white light and are more energy efficient and reliable than incandescent lamps, which they may replace in the near future. Devices optimised for the stimulated emission of coherent blue light are used as blue Laser diodes in the Blue Ray optical data storage format.

The story of Nakamura, who was awarded the 2006 Millennium Technology Prize as the inventor of new source of light, is not less exciting: He managed to convince his boss at Nichia to pursuit his search for the blue LED based on Gallium nitride, and, as the Chairman of the International Selection committee for the Millenium Prize explains,

Shuji Nakamura is a splendid example of perseverance and dedicated research work, and of making a major breakthrough. He has worked with great determination for decades, and even severe setbacks have not prevented him from achieving something that other workers in the field regarded as almost impossible: using a reactor system of his own design to develop a solid material, in this case gallium nitride, into a powerful light source producing blue, green and white light, and also creating a blue laser.

Blue Laser Diodes by Joachim Piprek is a freely available review about practical examples of GaN laser simulation, analysis, and optimisation, but gives also some general background on the GaN based blue LED technology.

Solid-State Lighting, the use of LEDs for lighting, has huge prospects because it is more energy-efficient than using usual incandescent or fluorescent lamps, and because LEDs are becoming ever cheaper and more durable. More information can be found, e.g., in Physics Today, December 2001: The Promise and Challenge of Solid-State Lighting (doi 10.1063/1.1445547), and at this page on Solid-State Lighting of the U.S. Department of Energy - Energy Efficiency and Renewable Energy - check out the PDF files.

Monday, October 15, 2007

One of the biggest annual fairs in Frankfurt took place last week - and for me, the most interesting anyway: the International Frankfurt Book Fair.

It's a huge event, in fact the biggest of its kind worldwide: 7500 exhibitors from 108 participating countries displayed nearly 400.000 different titles, according to the organiser's statistics, and the event attracted some 280000 visitors. There is always a Guest of Honour - usually a country, but this year it was The Catalan Culture, which had stirred a bit of trouble before.

On Saturday and Sunday, doors are open for the general public, and with the splendid weather, the fair ground transformed in kind of a big festival area. The exhibition halls with the German publishers are usually very crowded, but I love strolling around, and besides books, one can also spot celebrities.

But what I find most exciting is to wander around the exhibition halls of the foreign publishers. They are less congested, and there is a truly international flair, with all the different languages and cultures present at one spot. And there is a larger variety of, say, English or French books than one probably could find at any bookstore - plus, of course, books that haven't reached the bookstores yet.

Unfortunately - or luckily, depending on the shelf space available at your home - you usually cannot buy anything.

Sunday, October 14, 2007

The human memory works in funny ways. Yesterday, I thought of my first semester maths tutor, D. I really had a crush on him, awful. Some day, we happened to be alone together in the elevator. I had 25 floors to make a good impression.

We were just discussing complex numbers in maths. Parallel to this, the theoretical physicists had the harmonic oscillator on their schedule. And well, you know how it goes: plug in an exponential, find the complex solutions, take the real part. Sure, I could solve these equations, but I didn't understand where the imaginary part goes. If that question makes any sense. Plus I had learned Special Relativity with ict, which added to my confusion [1].

So, I asked D. why only the real numbers 'exist' and where the others are. (That means I must have found that a really good question.) 25 floors he had no way to get out of this.

This question came back to me yesterday when I read through your comments to The Mathematical Universe. See, as far as I know nobody has ever measured an observable to be a complex number. So whatever 'mathematical structure' constitutes the 'external physical reality' of our universe, complex numbers don't seem to be part of it [2].

However, we know that there are problems which can't be solved purely within the real numbers, say, take a square root of the Klein-Gorden equation. So the universe might try to evolve an initially real valued state, it wants to become complex, but the complex numbers aren't part of our 'external physical reality'. Then what? Do we get a cosmic error message? Does the unintelligent designer of our local patch in the multiverse get an F and fails the exam? Does the wave-function jump into another universe where the complex numbers exist, and then collapses back into ours?

Just asking.

The next time D. and I ran into danger of sharing the elevator, he had to use the bathroom really urgently. Gee, my whole life could have been different, if it wasn't for these complex numbers.[1] Still today, Wick-rotations seem like magic to me. Is there any good reason why that works?[2] Since we are dealing with complex numbers every day (well, some of us) this then means human thoughts are not real?

Saturday, October 13, 2007

FireRussell Maier's Fire Painting is a stunning collection of photos. Maier is a Canadian multi-media artist, who spends a couple of days carefully painting a canvas. He then covers it with gasoline soaked paper, lights a match to ignite it, and takes a photo of the flames. His art and digital photography is available for free download.

WaterMartin Waugh's Liquid Sculptures are a collection of great photos of drops in mid air. From the artist's statement: "Liquid Sculpture images are fluids in motion, frozen in time by a flash of light. They are droplets witnessed in mid-splash."

AirDan Wayland's skydiving photography from the skies of Texas and Virginia.

EarthJan von Holleben's photo series 'Dreams of Flying' is a beautiful collection of photos about flying while staying down on Earth.

Besides this: I will be travelling the next week, so you are facing a slow time on the blog.

Let me first roughly summarize what Tegmark says. To begin with there is the underlying assumption: Reality exists. This is a rather vague statement that nevertheless many of us seem to share, so I am willing to accept it [1]. Tegmark then formulates what he calls the ‘External Reality Hypothesis’:

He justifies this by saying mathematics is the right tool to get rid of the ‘baggage’ of our human existence, and is therefore the way to approach reality independent of human tainted thought:

“So here is the crux of my argument. If you believe in an external reality independent of humans, then you must also believe in what I call the MUH: that our physical reality is a mathematical structure. In other words, we all live in a gigantic mathematical object – one that is more elaborate than a dodecahedron, and probably also more complex than objects with intimidating names like Calabi-Yau manifolds, tensor bundles and Hilbert spaces, which appear in today’s most advanced theories. Everything in our world is purely mathematical – including you.”

and

MAT) “Whereas the customary terminology in physics textbooks is that the external reality is described by mathematics, the MUH states that it is mathematics.”

He further explains

B) “A mathematical structure is […] abstract entities with relations between them.” And that MUH applies “With a sufficiently broad definition of mathematical structure".Conscious beings like us appear within the mathematical universe as a specific kind of self-aware-substructure (SAS), that however has to cope with the problem of not having an overview on the whole universe. He calls that the ‘frog view’ and the ‘bird view’.

2. Think Maths

Indeed, I think of my job as describing reality with the use of mathematics. Therefore I find Tegmark’s hypothesis a bit disturbing. Despite (or maybe just because of) this, I find it also interesting. However, there is a good reason why I would say mathematics describes reality rather than it is reality.

To use a well known example, think of us as frogs in a cave with a fire where we can see only the shadows of ‘real’ things on the wall, like e.g. dancing Gods. Some of us frogs try to describe and understand these shadows, and we find drawings quite useful. After centuries of practice we get really good with the drawing. Since all the frogs sit on slightly different places, their drawings used to depend on their perspective. But after a lot of croaking they find a way to get rid of this froggy baggage. A couple of bright frogs even come up with interesting theories that make their drawings better descriptions of reality. E.g. they might invent some kind of interaction between the dancing Gods that explains a lot of seemingly odd behavior.

Now one of the frogs says these drawings are not descriptions of reality, they are reality. Quack, quack, quack, go the frogs. Obviously that can’t be. We can draw a lot of things that never appear on the walls.

Similarly, my problem with MUH is that I can observe a ‘real’ electron. I can think of it and describe it as a complex-valued wavefunction, a state in an ‘abstract’ Hilbert space. Now take away the electron. I can still think of and describe a complex-valued wavefunction. But that doesn’t make the electron ‘real’. At least I have the impression there is some kind of difference. If MUH is correct this could mean

Either our thoughts are not real. Which I could try to read out of Tegmark’s sentence “We humans can imagine many things that are mathematically undefined and hence do not correspond to mathematical structures”. This however would mean that the whole idea of the reality being mathematical is based on something not being real and mathematical, i.e. our thoughts. Which doesn’t give much credibility to hypothesis that mathematics is all of reality.

Or our thoughts are real. Then they are mathematical structures. But since human thought so far has to my best knowledge never produced an electron, our mathematical thoughts can only be very bad and insufficient descriptions of reality [2]. Which is kind of depressing to begin with, and in addition doesn’t give much credibility to the hypothesis that mathematics is all of reality either. (Saying that the electron I think of might exist in some other part of the multiverse doesn’t soothe me either since I actually want to describe reality here.)

Bottomline: MUH is founded on our ability to think of mathematical structures. Yet circumvents to explain the ‘real’ difficulty, namely the relation between thoughts and reality. This relation however is essential to the credibility of the hypothesis to begin with.

2. Word Worries

The statement MAT that external reality is mathematics is empty without explaining what mathematics is. One could equally well say whatever reality is, let's just call it mathematics. The formulation B is more concise. However, here the problem is shifted into the word ‘abstract’:

1. Considered apart from concrete existence: an abstract concept.2. Not applied or practical; theoretical. See synonyms at theoretical.3. Difficult to understand; abstruse: abstract philosophical problems

The open question remains whether there is ‘real’ mathematics (drawings of shadows) and ‘pure’ mathematics (drawings without shadows). To show that MUH has to follow from ERH, it is necessary but not sufficient to claim that mathematical structure is ‘with no baggage whatsoever’. One needs to know it is the only thing that can exist independent of human baggage.

I further have a problem with the reasoning of ERH implied in the word ‘independent’. We humans exist. If physical reality is a mathematical structure i.e. MUH holds, our existence has to follow from it – probably as kind of an emergent substructure. If it did not follow, physical reality was different, namely without us (you belong to my external physical reality). Thus, physical reality is not independent of us humans. Ergo, from MUH follows not ERH or from ERH follows not MUH.

You might call that nitpicking on words. It is. But it brings out the obvious fact that humans can not reliably state a formulation of reality which is independent of human ‘baggage’. The idea that we can do so is, well, an illusion. I.e. not ‘real’. Call that cognitive bias or The Principle of Finite Imagination.

Bottomline: Mathematics being without human baggage does not imply it is the only thing independent of humans, and therefore must constitute external physical reality.

He argues that we should take Darwin seriously and take into account that evolution did not train us to understand the universe, and that a fundamental description of reality therefore ought to seem odd and unintuitive to us. Interestingly, the very base of his hypothesis is that we humans are indeed able to grasp the foundations of reality, and that mathematics is the end of this leveling.

That might be true.

But maybe we should take Darwin seriously and take into account that there is no reason to believe our brains must be capable to understand true ‘reality’. The fact that we find mathematics an extremely compelling and powerful tool does not mean there is not level beyond it. So how about

Level 5: Beyond Mathematics

Can we possibly describe everything about the electron with mathematics? Can we ever be sure we describe everything about the electron? What is reality? The idea of loosing human ‘baggage’ with using mathematical calculus is nice. But it ignores the fact that my - and I believe also Tegmark’s brain - is entirely human. To date nobody has given a definition of mathematics that is not filtered through what our brains are capable to do.

Bottomline: We have no reason to believe that our brains are capable to grasp fundamental reality.

4: The Initial Conditions

Tegmark argues MUH resolves the problem with initial conditions. Mathematical structures just ‘are’, and since all of them ‘are’ ‘somewhere’ in the Level 4 multiverse, we don’t need initial conditions to describe reality:

“The MUH leaves no room for ‘initial conditions’, eliminating them all together.”

I like to think of the the universe being very well described by mathematics. That must not necessarily be a description by an evolution equation. I can imagine a mathematical description that just ‘is’ (and time is an illusion anyhow). That is to say the fundamental law might just not be a differential equation.

However, us being frogs means we sit somewhere inside this universe. The question we will typically ask is not ‘where are we?’ – which would then allow us to explain everything around us – but ‘how do I get from here to there?’. That is we are asking for a differential equation, a propagator, an evolution law. We measure here and now, apply our law, and get there and then. We have done that for centuries, and it works quite well. It requires however initial conditions. So this procedure might fail if we’re up to describe something like the whole Froggyverse.Instead, we could ask ‘where are we?’ and try to go beyond an evolution law. For this one doesn’t need to assume MUH. However, we might have gotten rid of the initial conditions, but instead we now need to specify our location. The argument is then the familiar one: since everything ‘is’ somewhere, one doesn’t need to specify anything. Just that instead of finding the Lagrangian for the TOE we now need to find a measure that explains why we are ‘where’ we are.

So to me it doesn’t solve any problem, it just puts the frog into a bird’s perspective. However, a different perspective can turn out to be useful nevertheless.

Bottomline: Interesting way to get rid of the initial conditions that could turn out to be useful, but does not depend on reality being mathematical.

5: Summary

Despite the impression that you might have gotten I like Tegmark’s hypothesis because it is quite minimalistic. Usually we deal with mathematics but only part of it is ‘applied’ to reality. We have maths, and we have a reality, both of which needs to be specified. If both was identical one could drop this additional complication. I also find the idea really neat that every time I make up some mathematical ‘relations’ between ‘abstract structures’, I am actually describing a real universe – somewhere.

However, I see my task as describing the universe around me. I have little doubt that for some while mathematics will remain useful for this, and I don’t think whether or not mathematics is real makes a practical difference [3]. I just don't find the hypothesis that reality is mathematics well motivated, since it is evidently constructed by humans. We have no reason to believe that this approach is indeed independent of human baggage, neither do we have any reason to believe it is the only way to describe reality.

It is nevertheless an interesting hypothesis, and might indeed lead to some insights. Sometimes a change of perspective is all it takes to make frogs fly.

See also: Christophe's post on MUH[1] I want to point out that the question whether or not reality exists is not subject of discussion, but a more or less plausible assumption. I.e. unless you can prove or disprove the existence of reality, please spare me the comments.[2] I could imagine that self-aware structures do carry around local versions of maths space with simpler structures.[3] Except for a headache possibly.TAGS:MATHEMATICS, SCIENCE, PHILOSOPHYMax Tegmark (2007). The Mathematical Universe Foundations of Physics, 38 (2), 101-150 DOI: 10.1007/s10701-007-9186-9

It has been a long time since there had been such a couple of prizes awarded to Germans.

About Grünberg, the Darmstadt local newspaper reported today that one of his professors, back at the time when Grünberg was a PhD student in Darmstadt, told him that he would once win the Nobel Prize, because he was up at the institute so early in the morning.

It seems that Grünberg has always been a very hard worker - in an interview on German TV yesterday evening, he said that he had had regular 14-hour workdays in the lab. I guess that is something that is often easily forgotten, that most prizewinners are extremely hard-working people.

The German Physical Society has presented the Stern-Gerlach-Medaille, its most prestigious award in experimental physics, to Grünberg earlier this year, and the Physik Journal (the German equivalent of Physics Today) reports the awardee's talk at the spring meeting of the DPG, Kopplung macht den Widerstand, by Peter Grünberg, Physik Journal6 (2007) No 8/9, 33. The PDF (in German) is for free.

Monday, October 08, 2007

The 2007 Nobel Prize for Physics will be announced tomorrow, Tuesday, October 9, 11:45 a.m. CET (at the earliest), for more info see nobelprize.org. You're welcome to let me know your guess.

The October issue of Discover Magazine is about 'The State of Science in America' and has a very readable essay by Lisa Randall who makes her points well: "More people, both within government and without, need to understand scientific data and the underlying statistics sufficiently well to make informed decisions." After addressing the problem that "American commitments can be unreliable" and "[m]any worthwhile projects are now happening overseas", she nevertheless remains optimistic "Also encouraging is the genuine thirst for knowledge in the public at large [...] Much of science is difficult to understand these days, but many make the effort to bridge the communication gap and teach or learn about new developments."

Unfortunately, the article is not online available. What however is online available are the illustrations of the issue that were selected in a contest among kids grade 3-8. I especially like the one below by Maya Gouw. Note the guy with the thought bubble 'Can't stop thinking'.

Africans have developed social rules to communicate via intentional 'missed calls' on mobile phones, called 'beeping'. They just let the phone ring until the name shows up on the display, then hang up and wait to be called back. Rules for the game include "richer guy pays" or "If you are chasing after a lady, you cannot beep". See: Rules of beeping at SciAm blogs.

One factor that sets humans apart from other species is our ability to exchange information fast, efficiently, and over potentially long distances in space and time. Another factor is the time spent with useless distractions. For evolutionary purposes drawings on the cave wall seem pointless since they don't keep the bears away. You might want to argue the prehistoric man meant to lure women into his cave, but why would they have a thing for painters to begin with?

It is no coincidence that our communication skills and art have develop hand in hand, and accompanied the progress of our civilization. The better we came to understand and utilize nature, the more time was freed from our struggle to survive, was freed for art and science. Above all I think of art as a form of communication. It doesn't have to be beautiful or pleasant, it ought to tell you something.

A picture paints a thousand words...

... is what they say [1]. If a painting has to come with a ten pages brochure so I understand the painter's intention, why then didn't the artist become a writer? However, to understand a painting the historical and sociological context is important, and it often happens to me that a painting only 'makes sense' after reading the blurb. Either way, a painting might tell you something, but not me, so that's why I don't argue about art (unless I have to see it every day).

"Music . . . can name the unnameable and communicate the unknowable.”

~ Leonard Bernstein

If you dream of being famous you better get a guitar instead of an easel, and become a rock-star. Why? Because people have radios in their cars, but rarely paintings. More importantly, evolution comes back into the game. Being famous definitely raises your chances in the gene pool

"To all you Sharons and MichellesWith all your tales to sellSave your meat money wellI'm glad that spending a night with meGuaranteed you celebrity."

~ Robbie Williams

But seriously, there must have been more than one women who was enchanted by the right iPod play-list [2].

... make the man. Sure, your clothes DO communicate. Things they say are possibly: 'Had eggs for breakfast', 'I'm colorblind', 'My wife picks my clothes', or 'I believed the shop assistant'. Well, I am not a fashion geek. As many other design forms, fashion needs to balance creativity with functionality. And my preferences are definitely on the side of functionality [4]. I have genuinely no idea what modern fashion shows are supposed to tell me. To the right you see an example of the 2008 spring/summer menswear [John Galliano]. Just so you know what's en vogue.

... well, this is list is certainly not exhaustive, there's numerous other forms for artists to express themselves, may that be in architecture, sculptures, or scriptwriting. And new mediums are explored all the time. The most intriguing aspect of art is its potential to access communication channels that many people share. Art can escape the constraints of language or photos, and it constantly re-creates itself.

The Web

Technological progress offers new playgrounds also for artists, like raytracers, java applets or images obtained by sheer computing power. Admittedly, not all of this tells me very much. What is depressing for me is that the biggest part of the www is not only ugly, but most design doesn't really promote information exchange. By now many websites are filled up with advertisements, up to the level of being completely dysfunctional.

Bottomline

So why did the cave man paint the walls? Because it allowed him to pass on information, possibly over many generations - and that without luring the women into his cave. And why did the woman fall for it? Well, because we like cute little animal pictures, and men who know to express themselves.

Given that communication is one of our most important strengths, I hope we come to pay more attention to its efficiency. We don't need more web-designers who invent even more clever ways to pop up advertisements, but the www could certainly use some style (says the women wearing jogging shorts and an oversized PI - shirt).

PS: No meta messages.[1] The equivalent German proverb is 'Ein Bild sagt mehr als 1000 Worte'. [2] Previously: self-recorded tape.[3] This post is actually a warm-up for a post on Art and Science, but well. I guess I've successfully spent my time on useless distractions ;-)[4] Modern Version.TAGS:ART, COMMUNICATION

Sunday, October 07, 2007

... that the can opener was invented 48 years after invention of the can?

Food preservation in cans was patented in 1810 by the British merchant Peter Durand. The first commercial canning factory was opened in England in 1813. In 1846, tin cans could be manufactured at a rate of sixty per hour.

However, though Durand had figured out how to seal food into cans, he just left the consumer with the instruction: "Cut round the top near the outer edge with a chisel and hammer." [Source] This was complicated by the fact that the first tin-coated iron cans were made of thick metal, and often weighed more than the food they held. Usually, the cans were opened with heavy equipment by the clerk in the grocery store [Source].

The first can opener was patented in 1858, by Ezra Warner, and looked like a bent bayonet. It had the big advantage that the user pressed, rather than stabbed it, into the can. A metal guard kept the point from penetrating too far, to “perforate the tin without causing the liquid to fly out.” A second, curved blade could then be worked around the rim to finally remove the lid. Warner’s patent even claimed that “a child may use it without difficulty, or risk.” [Source]

It was only when thinner steel cans could be manufactured in the 1860s that a useful can opener could be invented. In 1866, J. Osterhoudt patented the tin can with a key opener that you can still find today on sardine cans [Source]. And the picture to the right shows a 21st century version of the can-opener.

I wonder whether, in some basement in England, there is a tin can with mixed pickles from 1812 (that however nobody can open with Black&Decker).

So, if you have a great idea don't forget instructions how to open the can, and keep in mind it might take some decades for the details to work out.

Thursday, October 04, 2007

The small dots denoted by the arrows on this photo are 34 out of about 240 geostationary satellites, orbiting Earth at an altitude of 35,786 km above ground, where the orbital period is 24 hours and a satellite appears to be fixed at a spot above Earth's equator. The image shows a strip of roughly 30° along the celestial equator. During the 8.5 hours of exposure at Kitt Peak, Arizona, the stars in view moved along their usual paths in the sky, and left the bright trails. (Credits: Dave Dooling, National Solar Observatory, Tucson, Arizona; from Earth Science Picture of the Day (EPOD) from September 4, 2007)

On October 4, 1957, a team of Russian engineers and scientists successfully put the the first man-made satellite into an orbit around Earth. Sputnik 1, the "fellow traveller", transmitted a simple radio signal while circling the Earth once every 96 minutes at a height between 215 and 940 kilometres. Sputnik was visible through binoculars in the sky: TIME magazine told its readers on October 14 that "the satellite's orbit shifts around the earth at 4° per day. This will bring it over the U.S. at twilight on about Oct. 20, when it should be visible through small telescopes or binoculars."

50 years later, the sky is full of satellites, for communication, navigation, observation of the weather, military reconnaissance, and the transmission of more television channels than I ever wanted to see. And satellites in low orbits are not difficult to see by the naked eye:

I was surprised, when spotting Perseids in August this year, that I could see nearly as many satellites as meteors. On a clear night about two hours after sunset, just watch out for faint, steady lights travelling on straight paths among the stars. If the light does not blink, chances are high that it's a satellite, not an airplane, and if the light fades away when reaching the Eastern parts of the sky, you can be sure it was a satellite: it has reached a point where even at a height of a few hundred kilometres above ground, it has eventually entered the Earth's shadow that is the night.

I was even more surprised when I came across the photo on the left, showing 34 satellites at a height of 35,786 km above ground in geostationary orbits. While these satellites are quite bright at radio frequencies, and are observed on a regular basis by hundreds of millions of radio dishes all around the world, they are a hundred to ten thousand times dimmer than the faintest stars visible to the naked eye, so that it takes a telescope and quite a long exposure to catch them on film.

Including the geostationary satellites and the low-orbiting ones visible to the naked eye after nightfall, about 850 active satellites are in orbit today. The article Space debris by David Wright in the October issue of Physics Today (doi: 10.1063/1.2800252) gives an interesting breakdown of the current satellite population according to usage, orbital altitude, and country. More than half of the satellites currently in use are from the US, and from the total number of satellites, 15% are used for science, and 66% for communication. But the main intention of the paper is to point us to the huge number of debris orbiting the Earth: scraps of defunct satellites, rocket parts, gloves of astronauts - more than 700,000 pieces larger than 1 centimetre are rushing around, and may pose a serious risk to satellites or the space station.

But already when looking at the satellites currently in operation, the sky looks quite crowded: The NASA Satellite Tracking website features a Live 3D Java Tracking Display (as the name implies: Java required), which provides an interactive 3D visualisation of satellites and their orbits around Earth. I didn't know the the GPS satellites actually have quite high-lying orbits, at altitudes of about 20,000 kilometres above ground. In case you now the exact name of a satellite, detailed information about the orbit are available also from the Select Satellite form at Heaves Above.

50 years after Sputnik, Space below the geostationary orbit has become quite crowded. Fortunately, it is still wide enough.

The New York Times commemorated the launch of Sputnik with several articles in Science Times: The Space Age in the issue of September 24, 2007. Moreover, at The Times looks back: Sputnik, we can follow the original coverage of Sputnik 50 years ago, starting with the headline and cover story of October 5, 1957, "Soviet Fires Earth Satellite Into Space; It Is Circling the Globe at 18,000 M.P.H.; Sphere Tracked in 4 Crossings Over U.S." The NYT had even shown the orbit in a figure on the title page.